Fail-safe vital relay contact arrangement



March 18,1969 A. HUFNAGEL FAIL-SAFE VITAL RELAY CONTACT ARRANGEMENT Filed Oct. 25, 1967 Sheet ofz [MT/V0702 flu/12039 6.

. m T w 1} e .G 4 m@ M kw law 3 1 LR V [I I! an. L MI M I INM E a F T L R 1 mm: 1$ Q R MW x Q N mm Q 1 .NM 1 T .1 &\|l\ M r w: LI PIIII|||1|ll|||lI||ll| L| lll||||vI.l||||| I|.Y HWN RN llllllllllllllllllllllllllllll lli Q Q MW W H15 1 JTORW A. HUFNAGEL March 1 8, 1969 FAIL-SAFE VITAL RELAY CONTACT ARRANGEMENT Hi5 Array? Sheet lindvew [leaf/2 3 Filed Oct. 25, 1967 I United States Patent 6 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a fail-safe vital relay contact arrangement. The construction of the front, heel, and back contact members is such that should the back and heel contacts become welded together during operation of the relay, they will never be able to make additional contact with the front contact member because the heel contact member is constructed to include a notched region which only allows pivotal flexure coupled with column rigidity of the remaining portion of the heel contact member to prevent the physical excursion of the welded contacts sutficient to make electrical contact with the front contact.

This invention relates to an improved vital relay contact arrangement.

More specifically this invention relates to a fail-safe vital relay Contact arrangement which includes a front contact member, a heel contact member, a back contact member and a heel contact member driver. Fail-safe cooperation is provided between the heel contact of the heel contact member, the front contact of the from contact member and a back contact of the back contact member if the heel contact and the back contact become Welded to each other during operation of the relay. This is accomplished by providing the heel contact member with a structure that has uniform thickness throughout its length with the exception of a reduced thickness region near the end of the heel contact member where the heel contact is secured at the relay frame. The reduced thickness portion has a length dimension such that there can only be a pivotal flexure in the region of the reduced thickness region due to the combined column regidity present in the uniform thickness portion and the absence of column buckling in the reduced thickness portion, In the event that the heel contact and the back contact should weld together, the heel contact member and the related welded contacts are restrained in the total distance they may travel toward the front contact due to the heel contact members column rigidity and the pivotal flexure present in the reduced thickness region.

In a vital relay should a back contact and a heel contact weld together, they must never be so constructed as to allow the welded pair of contacts to make an electrical connection with a front contact while in this welded condition. To this end many efforts have been expended in the prior art and while success has been achieved it has almost always been accomplished by mechanical arrangements in contact structures that required the utmost precision in manufacture and adjustment during assembly. Escalating costs plague the industries that manufacture such relays. In order to reduce such costs significantly the invention to be described provides a solution with advantages that elevate this contribution into the realm of invention.

It is therefore an object of this invention to provide a fail-safe relay contact structure that guarantees that, should the heel and back contacts become welded, the welded contacts will never make electrical connection with the front contact, all of this to be accomplished by the utilization of a heel contact member configuration which cofunctions with both front and back contact members as well as an armature driven heel contact driver element to thereby establish the protection required.

It is another object of this invention to provide an improved front contact structure that further enhances the fail-safe qualities of the improved contact arrangement.

In the attainment of the foregoing objects the improved vital relay contact arrangement includes a front contact member, a heel contact member, a back contact member and a heel contact member driver of insulating material. The vital relay contact arrangement provides a fail-safe cooperation between a heel contact of the heel contact member, a front contact of the front contact member and a back contact of the back contact member, whenever the heel contact and the back contact become welded to each other during operation of the relay.

The front contact member has a first rigid portion secured at one end to an insulating block and a second resilient portion secured at one end thereof to the first rigid portion and at the other end thereof is a front contact tip. The back contact member has a first rigid portion which is secured at one end to the insulating block and a second resilient portion secured at one end thereof to the first rigid portion and at the other end thereof is a back contact tip.

The heel contact member is disposed intermediate the front and back contact members and is secured to the same insulating block. The second resilient portions of both the front and the back contact members are permanently biased toward each other, whereby the alternate electrical connection between the heel contact and the front and back contacts produces a wiping action between contacts due to the biased condition and the resilient nature of the resilient portions of the front and back contact members.

The heel contact member has a uniform thickness throughout its length with the exception of a reduced thickness region near the end of the heel contact member where the heel contact member is secured to the insulating block. The reduced thickness portion has a length dimension such that there can only be a pivotal flexure in the region of the reduced thickness due to the combined column rigidity present in the uniform thickness portion and the absence of column buckling in the reduced thickness portion.

A heel contact is secured to the heel contact member and the contact driver is drivingly connected to the other end of the heel contact member so that when the drive member is moved during relay operation, the heel contact alternately contacts the back and then the front contact. In the event that the heel contact and the back contact should weld together, the heel contact member is restrained in the total distance it may travel toward the front contact due to the heel contact members column rigidity and the presence of pivotal flexure in the region of reduced thickness.

It is also significant to note that the heel contact is secured to the heel contact members portion of uniform thickness at a point intermediate the other end where the heel contact is drivingly connected to the heel contact driver, and the reduced thickness region.

An additional feature of the contact arrangement is a unique front contact which is a silver impregnated, silver plated carbon element which has a portion thereof which has been exposed by machining to present as a contact surface only the silver impregnated carbon. This front contact element is mechanically and metallurgically interconnected to the resilient portion of the front contact member to thereby provide an integral mechanical and electrical contact arrangement.

Other objects and advantages of the present invention will become apparent from the ensuing description of illustrative embodiments thereof, in the course of which reference is had to the accompanying drawings in which:

FIG. 1 depicts a D.C. vital relay which embodies the invention.

FIG. 1a illustrates in detail a front contact embodying certain aspects of the invention.

FIG. 2 is a series of schematic illustrations of a basic mechanical problem which the invention overcomes.

FIG. 3 sets forth a prior art contact arrangement.

FIG. 4 schematically illustrates a contact arrangement embodying the invention and FIG. 4a is an enlarged view of a portion of a heel contact member.

FIG. 5 schematically illustrates the mode of operation of a contact arrangement embodying the invention.

FIG. 6 shows a contact ararngement embodying the invention where a heel contact and a back contact have become welded during operation.

FIG. 7 depicts in exaggerated fashion a structural consideration involved in the application of the invention.

A description of the above embodiment will follow and then the novel features of the invention will be presented in the appended claims.

Reference is now made to FIG. 1 in which there is illustrated a portion of a DC. neutral relay embodying the invention. Basically, this relay functions in a similar manner to the relay shown and described in great detail in Letters Patent of the United States No. 2,836,774, granted to Harry E. Ashworth, on May 27, 1958, for Magnetic Hold-Down Devices. Basically, the DC. neutral relay has a coil 11 which has passing therethrough a core member 12. This coil 11 is electrically connected to a coil terminal finger 19. The electrical interconnection between this coil and terminal finger 19 is not shown but it is to be understood that when this plug-in type relay is pressed into position and the coil terminal finger 19 engages a terminal socket, the D.C. power supply will be connected to the coil 11 and accordingly produce a magnetic field within the core 12. The coil 11 and core 12 are mounted upon a relay frame 13 made of a nonmagnetic material, and the core 12 is secured by bolts 14 and 16 to the relay frame 13. In order that this relay may be readily removed from the plugged-in position and reinserted there is provided a handle 17, which handle 17 is secured by a screw 18 to the relay frame 13.

In addition, there is provided in this type of relay 2. permanent magnet structure 26, here shown as a single element for purposes of illustration and explanation. The permanent magnet 26, whose function will be described hereafter, is secured to the frame 13 by a bolt 27.

Within the frame 13 and shown in dotted outline are a pole piece 28 and a pole piece 2 9, each of these pole pieces respectively having pole piece extensions 31 and 32. The under surface of the pole piece extension 32 has a pole face 34, and the pole piece extension 31 has a pole face 33. Immediately beneath the pole faces there is an armature structure 36. This armature 36, its construction and mode of operation are described in greater detail in my copending application for Letters Patent of the United States, Serial No. 677,924, filed October 25, 19 67, for Improved Relay Armature Arrangement. The armature 36 has at its left-hand portion a fulcrum point 37. This fulcrum point 37 has been formed by the beveling of a surface on the left-hand end of the armature 36. The beveled surface 38, as it meets with the upper surface of the armature, provides the fulcrum point 37 about which this armature will pivot.

Also secured to the frame 13 is a hinge block 39, which hinge block 39 has a depending ledge portion 44 which extends underneath the end of the armature 36. The hinge block 39 is secured to the frame by a bolt 41, and there is an extending portion 45 of the hinge block 39 which also 4 extends underneath the end of the armature 36. There is provided a helical compression spring 42 between the armature 36 and the hinge block extending portion 45. This helical spring 42 is maintained in position by spring retaining opening 43 in the armature 36 and by spring retaining opening 44 in the hinge block extending portion 45. This helical compression spring provides substantially all of its force directed through the fulcrum point 37 of the armature 36 and forces the armature toward the coil and core structure 1112 which forms an electromagnetic means.

The armature 36 has sandwiched between its fulcrum point and the pole face 34 of the pole piece extension portion 32 a spacer 51 as well as a flat, plate-like hinge spring 52. The flat, plate-like hinge spring 52 is secured at one end to the armature 36 by a screw 53. Between the screw 53 and the hinge spring 52 is a spacer 54. The hinge block 39 has also sandwiched between the pole face 34 and the hinge block 39, the spacer 51 as well as the hinge spring 52.

The armature 36 also has at its right-hand end an armature stop pin 56, the function of which will be explained hereafter. Secured on the bottom side of the armature 36 is a contact driver bracket 57, which bracket 57 is secured by a screw 58 to the bottom of the armature 36. There is connected to the bracket 57 a heel contact driver 59 of insulating material, which heel contact driver moves in unison with the armature 36 whenever the relay coil and core have been energized in a manner to be described hereafter. Secured to the frame 13, by means not shown, is an insulating contact block 61. Passing through the insulating contact block 61 is a rigid front contact portion 62. The rigid front contact portion 62 has sandwiched within the front contact portion a front contact spring which has an extending front contact spring portion 63, or resilient portion as it may be termed, which terminates in a silver impregnated carbon front contact tip 64. While not shown in this figure, it will be understood that the front contact spring 63 is electrically integral with a front contact terminal finger 66 shown to the left of the contact block 61.

There is also depicted here a heel contact terminal finger 67, as well as a back contact terminal finger 74, each of which is respectively electrically connected to a heel contact and a back contact to be now described. The heel contact has a rigid portion 69 through which passes the heel contact member 68. This heel contact member 68 has a machined slot 71 in a surface thereof adjacent the rigid portion 69. The function of this slot is explained in detail when FIGS. 4 through 7 are described hereafter. At the end of the heel contact member 68 is a heel contact 73 and the heel contact member 68 is secured to the heel contact driver 59 by a bendable clip 72. The back contact terminal finger 74 passes through the block 61 and is electrically secured to the back contact spring portion 76, or resilient portion as it may be termed, which spring is secured within the rigid back contact portion 77. The spring 76 terminates with a back contact 78.

The entire mechanism just described is housed within a housing 48, a portion of which is shown here. It is to be understood that the housing 48 completely surrounds the mechanism to maintain the relay free from dust and contamination. The housing 48- is a transparent plastic cover and is secured to the frame 13 by a screw 49. The relay shown here is in its rest condition. By this it is meant to convey the concept that when the relay is in its deenergized position the armature 36 is at rest upon a portion of the permanent magnet 26. The armature 36 is at rest upon the permanent magnet 26, due to the magnetic field present in the permanent magnet 26. The magnetic field created by the permanent magnet is depicted by the dashed lines 21 which show the permanent magnetic field passing upwardly through the pole piece 28, through the core 12 of the electromagnetic means, down through the pole piece 29, through a portion of the pole piece extension 32, and down through the hinge spring 52 and the fulcrum point area 37, into the armature 36, along the armature 36, and back into what is designated as a south pole of the permanent magnet 26. The designations S and N shown in this figure are for purposes of illustration to explain the relative polarity of the magnet 26.

When the relay has been plugged in and a DC. voltage energizes the coil 12, the electromagnetic field thereby created will take on the direction shown by the solid lines 22 which contain arrows depicting the relative direction of the electromagnetic field, and it will be appreciated that as the electromagnetic field increases in strength, the magnetic lines of force, namely, the electromagnetic field as shown by the arrows 22 and the permanent magnetic field shown by the arrows 21, will oppose each other. When the electromagnetic field exceeds the permanent magnetic field, the path of the electromagnetic field will be downwardly from the core 12 through the pole piece 28, through a portion of the pole piece extension 31, into armature 36, along the armature 36, upward to the fulcrum point area 37, and into the pole piece extension 32 and pole piece 29, and rfinally back into the core 12. Of course, when the coil 11 is deenergized, the electromagnetic field collapses and the permanent magnetic field, shown by the dotted lines 21, becomes of a strength suflicient to pull the armature 36 back into its rest position on the permanent magnet 26, as is depicted here.

Reference is now made to FIG. 2 which illustrates in schematic form a relay contact arrangement without the employment of the invention and the problems that arise as a result of excluding the invention that is to be described more fully hereafter.

The first arrangement at the top of FIG. 2 shows a front contact 63a, heel contact member 68a, and back contact member 76a. In this portion of the figure, as well as other portions of the figure, wherever reference numerals denote similar parts as those described with reference to FIG. 1, the character a has been added in order to designate the fact that they pertain only to the environment shown in FIG. 2. Accordingly, there is a contact block 61a to which is secured the front contact rigid portion 62a as well as the back contact rigid portion 77a. The heel contact rigid portion 69a is also disposed in a manner similar to that rigid portion shown in FIG. 1.

The first illustration at the top of FIG. 2 shows a situation where a heel contact driver 59a is in a neutral position. At this point the heel contact 73a is shown midway between the front contact 64a and the back contact 7 8a. The resilient portions of the front contact member 63a and the resilient portion 76a of the back contact are biased in the direction of the heel contact 73a which is carried by the heel contact member 68a.

In the second illustration, which appears in the middle of FIG. 2, there is depicted the situation where the back contact 78a and the heel contact 73a have been moved into electrical connection by the movement of the heel contact driver 59a downwardly as the arrow depicts in this portion of the figure. As one may appreciate from a study of this middle portion of FIG. 2, the heel contact member is of uniform thickness and would bend in a general arc downward toward the back-contact 78a under the influence of the movement of the heel contact driver 59a. This operation of course would be perfectly satisfactory except for the situation that arises when, as shown in the lower portion of FIG. 2, the heel contact 73a becomes welded to the back contact 78a. Under this situation when the heel contact driver 59a moves upward, the heel contact driver 59a will attempt to move the welded contacts 73a and 78a upward toward the front contact 64a. Since the element 76a, namely, the resilient portion of the back contact member, cannot be stretched under the type of loadings that exist here, the end of the contact 78a is limited in its basic movement into an are shown by the arrow which passes through the back contact 7811. Since the spring element or resilient portion 760 of the back contact cannot stretch and must pivot in the manner shown, the only way that the combined fused contacts 73a and 78a may come into electrical contact with the front contact 64a is for the heel contact member 68a to buckle. This buckling action is induced by the force as shown by arrow 90, and the presence of this force and the buckling of the column-like structure of heel contact member 68a reduces the distance between the heel contact 73a and the rigid portion 69a of the heel contact member. In so doing the back contact 78a which is fused thereto may in fact pass through the arcuate travel shown by the arrow through the welded contact arrangement, and in so doing allow the heel contacts 73a and 78a to cause a failure when they mutually come into electrical contact with the front contact 64a. The obvious solution to this problem, of course, might be to increase the thickness of the heel contact member 6811. When this is done the rigidity of the heel contact member 68a gets to a point where the force required to flex the heel contact member 68a about the point where the heel contact enters the rigid portion 69a creates an overall structure that will be too stiff, and therefore this approach becomes unacceptable.

In FIG. 3, there is shown a prior art arrangement in which a thicker heel contact element 97 is employed and in which there has been a notch made in the heel contact member 97 near the base of the heel contact member adjacent the insulating block 93. Note here that in this arr-angement which is shown in Letters Patent of the United States No. 2,258,122, granted to I. F. Merkel, on October 7, 1941, for a Relay, and described in great detail therein, the driver contact member is positioned intermediate the contacts that are at the end of the front contact member 96 and the back contact member 98, as well as the heel contact member 97, between the contacts of these members and the base 93. When the contacts of the heel contact and the back contact are fused, the upward movement of the heel contact driver causes the heel contact member to flex in the middle, as shown, and while the action is not one of buckling it actually may allow the fused back contact and heel contact to come into electrical connection with the front contact of the front contact member 96.

Note also that this prior art arrangement requires a multitude of spring arrangements 99 on the back contact as well as the front contact. These springs, of course, over long usage create problems of wear and adjustment as resiliency changes with time and the number of flexures experienced spans many years of use.

Reference is now made to FIGS. 4 through 7. In these figures there is depicted in schematic form the basic elements of the improved contact arrangement. Wherever the reference numerals are directed to portions that were heretofore described with reference to FIG. 1, these reference numerals will be used again. It will therefore be seen in FIG. 4 that secured to the insulating block 61 are both the front contact rigid portion 62 and the back contact rigid portion 77, as well as the heel contact rigid portion 69. The front contact member has the biased resilient portion 63 which has at the end thereof a front contact 64 schematically shown as a simple contact structure. The back contact member has a biased resilient portion 76 and at its end a back contact 78. The heel contact member 68 as shown schematically at its right-hand end a contact driver 59 which causes the heel contact member to move upward and downward into and out of contact with the front contact 64 and the back contact 78, as the heel contact 73 makes respective contacts with the afore noted contacts.

Shown within a circled portion of the heel contact member is a slot or opening or space that has been machined in the surface of the heel contact member 68. This has been designated by the reference numeral 71 and shown in expanded detail in FIG. 4a where the presentation in FIG. 4a shows a magnified view of this portion of the heel contact member. There is also shown in FIG. 4a, as well as FIGS. 5 and 6, a dot and dash center line which passes through the middle of the slotted portion 71. It is about this center line which the heel contact member 68 pivots and is about which point the pivotal fiexure necessary to allow the contact member 68, as well as its contact 73, to move in what will be a fail-safe manner.

Note when FIG. 5 is viewed that the heel contact member 68, while shown in this figure in intimate electrical contact with the back contact 78, is actually straight and that the flexing that occurs is actually in a pivotal fashion about the center line depicted through the slotted portion 71. The heel contact member does not bend in the conventional sense in that it is bowed but actually moves in a straight column between the front contact position shown in dotted outline and the back contact position shown in solid lines. It is this column-like pivoting fiexure of this member that allows this arrangement to provide the fail-safe operation afore noted. For it will be appreciated as FIG. 6 is viewed that the slot 71 in the heel contact member 68 coupled with the column rigidity of the heel contact member 68, as it co-functions with the heel contact driver 59, creates a situation where the heel contact member 68 has sufficient column strength to resist the column buckling of the type depicted in FIG. 2. Since the heel contact member cannot enter into a column buckling mode when the heel contact 73 becomes Welded to the back contact 78, the heel contact driver 59 is limited in its upward movement. In fact, it has been found that the heel contact 73, when welded to the back contact 78, can go no further in its upward movement than that shown in this FIG. 6. Therefore, once these two cont-acts become welded the column strength of heel contact member 68 is such that it will not buckle, and since the back contact resilient portion 76 will not stretch under the force imposed thereon by the welded contacts 73 and 78, the relay switch remains as it is shown in FIG. 6 without the failure that has transpired in both of the situations depicted in FIG. 2 and FIG. 3.

Reference is now made to FIG. 7 in which the base portion of a heel contact is shown. To these reference numerals there has been added the character b designating the fact that this figure is intended to show a physical configuration that differs from FIG. 1 and FIGS. 4 through 6. This configuration should be avoided at all costs. Note that if the slotted portion 71b of the heel contact member 68b is made of too great a length, then, as shown in the bottom portion of FIG. 7, the forces that appear doWnwardly along the heel contact member 68b, as shown by the reference arrow 7011, can cause the slotted portion if it is too long to experience a buckling action as shown by the reference numeral 75. If this buckling action should ensue because the slot is made too long, then the fact that there is a pivotal action present, coupled with the buckling action shown designated by the reference numeral 75, will allow the shortening of the heel contact member 6812 and therefore allow a failure of the type shown in the bottom portion of FIG. 2. Therefore, it is important to recognize that the slotted portion that appears in the heel contact member must not be so long as to permit a physical buckling of this during the operation of the relay contacts when there is a welded condition experienced due to malfunctioning. The slot must only be of a width sutficient to allow the pivotal fiexure of the heel contact member as is shown in FIG. 6.

Reference is now made again to FIG. 1a which shows the front contact 64 of the front contact member 63. This front contact is unique in that it has been produced by the process of taking a piece of silver impregnated carbon and silver plating the entire piece. Then, as can be seen in FIG. la there is a need for a beveled surface 65 on the front contact. This beveled surface is accomplished by machining through the contact tip 64 to expose a silver impregnated carbon surface. This silver impregnated carbon surface then is the contact surface of the front contact 64, and the purpose of removing the plating is to expose a carbon surface which, as has been proven by past experience, cannot become welded to a silver contact such as contact 73. All the remaining surfaces of the front contact are silver plated, as has been noted, and afford maximum electrical and mechanical continuity When this front contact tip is soldered to the resilient front contact member 63. In addition, there is shown mechanically secured to the front contact tip 64 a bracket 60, which bracket 60 provides additional mechanical in terlocking of the front contact tip 64 to the resilient portion 63. A solder connection between the front contact resilient portion 63 and the silvered surface of the front contact tip 64, as well as the mechanical interlocking, provides an extremely reliable contact.

In practice, solder is applied at a, which in addition to anchoring the ends of bracket 60, flows through hole b in resilient member 63 and appears at 0, along the end of resilient member 63, to indicate that solder has flowed in such a fashion as to properly solder member 63 to the top silver plated surface of front contact tip 64.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

Having thus described my invention, what I claim is:

1. An improved vital relay contact arrangement in which there is included a front contact member, a heel contact member, a back contact member and a heel contact member driver, said vital relay contact arrangement having a fail-safe cooperation between a heel contact of said heel contact member, a front contact of said front contact member and a back contact of said back contact member, when said heel contact and said back contact become welded to each other during operation of said vital relay,

(a) said front contact member having a first rigid portion and having said first rigid portion secured at one end to an insulating block and a second resilient portion secured at one end thereof to said first rigid portion and having at the other end thereof a front contact tip,

(b) said back contact member having a first rigid portion and having said first rigid portion secured at one end to said insulating block and a second resilient portion secured at one end thereof to said first rigid portion and having at the other end thereof a back contact tip,

(c) said heel contact member disposed intermediate said front and back contact member and secured to said insulating block,

said heel contact member having a uniform thickness throughout its length with the exception of a reduced thickness region near the end of said heel contact member where said heel contact member is secured to said insulating block, said reduced thickness portion having a length dimension such that there can only be a pivotal fiexure in the region of said reduced thickness due to the combined column rigidity present in said uniform thickness portion and the absence of column buckling in said reduced thickness portion,

a heel contact secured to said heel contact member and said contact driver drivingly connected to the other end of said heel contact member so that when said drive member is moved during relay operation, said heel contact alternately electrically interconnects said back and said front contacts, in the event that said heel contact and said back contact should weld together said heel contact member is restrained in the total distance it may travel toward said front contact due to said heel contact members column rigidity and said pivotal flexure in said region of reduced thickness.

2. The improved vital relay contact arrangement of claim 1 wherein said second resilient portions of said front and said back contact members are permanently biased toward each other, whereby said alternate electrical connection between said heel contact and said front and back contacts produces a wiping action between contacts due to the biased condition and the resilient nature of said resilient portions of said front and said back contact members.

3. The improved vital relay contact arrangement of claim 2 wherein said heel contact is secured to said heel contact member portion of uniform thickness at a point intermediate said other end where said heel contact is drivingly connected to said heel contact driver and said reduced thickness region.

4. The improved vital relay contact arrangement of claim 3 wherein said front contact is a silver impregnated, silver plated carbon element having a portion thereof which has been exposed to present as a contact surface only of said silver impregnated carbon,

said contact element mechanically and metallurgically interconnected to said resilient portion of said front contact member to thereby provide an integral mechanical and electrical contact arrangement.

5. The improved vital relay contact arrangement of claim 4 wherein said reduced thickness region is a machined slot and said heel contact member has a fiat plate configuration of uniform width throughout its length.

6. The improved vital relay contact arrangement of claim 5 wherein said heel contact driver passes through an opening in said heel contact member and is held in driving cooperation with said heel contact member by a single bendable clip.

References Cited UNITED STATES PATENTS 2,591,684 4/1952 Deakin 200-166 2,853,578 9/1958 Rommel et a1 200166 2,939,932 6/1960 Walter 200-466 2,959,693 11/1960 Meyer 200166 3,283,109 11/1966 Korsgren 200166 3,337,707 8/1967 .lluptner et a1. 200-466 ROBERT K. SCHAEFER, Primary Examiner.

H. O. I ONES, Assistant Examiner.

US Cl. X.R. 

